LECTURES ON CHEMISTRY, BY PROFESSOR BRANDE

76

pro-1 of its inhabitants, in order to determine on and mineral the objects of his ulterior pursuits : for the kingdoms. Even the birds of rapid flight rudiments he has attained, equally qualify and delicious flavollr, are claimed by the him for accurate observation, and for the proprietor of the district through which higher energies of reflection. Having bethey pass, and the wilder quadrupeds are come familiar with the exercise of speech, equally the subjects of appropriation : these and with the construction of his native are moderate assumptions. But man him- tongue, he is more readily enabled to extend self becomes the object of a bargain :-he is his researches for the possession of others ; driven to the market, like an ox unto the and thus to imbibe, from their immediate slaughter ;-his fine proportions are eulo- sources, the eloquence and wisdom of the gised by the appraiser, his prowess is dis- Grecian and the Roman models. On these played, and his abject submission warranted solid foundations he may erect the edifice of to enhance his price. Even sex claims no learning ; and by the patient devotion of his exemption from this iniquitous traffic, and mind to the standards of excellence, he may the offspring becomes the slave of the pur- surmount the difficulties of composition, and chaser. Such is the cupidity of man, that convey his opinions in perspicuous and con. He may seek advancewere his power unlimited, he would have nected sentences. mouopolised the host of heaven,-and sold a ment in the departments of the law,-or, planet by private contract, or knocked it directed by more solemn views, he may reo down to the highest bidder. The repre- luctantly aspire to the preferments of the sentatives of value are the multiplications or church :-and if his industry be equivalent subdivisions of a standard, and although they to his talent, he may be distinguished as an vary in different countries, are all ultimately honourable and skilful member of our own resolvable into numbers. The operation of vocation ;-a profession whose basis connumbers may be correctly considered either sists in the union of learning and of sci. as an abstract science, or as connected with ence ;-and whose superstructure is expethe useful purposes of our nature. The ad- rience expanded by reason, and condensed dition or substraction of figures may consti- by thought. tute a simple and process, or they may be conjoined to the forms of matter, to space, to time, or to value. Thus the I accurate chemistry of our own day is expressed in numbers, and in their fractional LECTURES ON CHEMISTRY, divisions. The admeasurements of the existing temperature of the atmosphere, together BY with its gravity and prevailing moisture, can only be indicated by a scale numerically PROFESSOR BRANDE, constructed. The specific weight of solids, fluids, and even of gaseous substances, can Delivered at the Royal Institution of Great only be characterised by number. The preBritain. paration of medicinal compositions, and their distribution into certain doses, and also the particular times when they are to be adLECTURE I. ministered, imply the numerical divisions both of weight and of time. It would be WE are assembled, here, Gentlemen, for useless to enumerate further instances of the purpose of commencing a course of lecthe indispensable application of numbers :- tures on Chemistry, and I shall endeavour to their utility becomes evident on the slight- state to you the objects of the science in est consideration, although their immense general terms, and to give you an account of power and higher employments have been the order of study which will be adopted. I need scarcely state to you that the term unnoticed. They are the immediate instruments of all ratios and computations, and chemistry was employed by the old chemists constitute the ground work of the whole to denote the science of the transmutation range of natural philosophy, and, on a future of the metals, and the conversion of the vaoccasion, will be exhibited as the basis of rious metallic bases into gold ; and the alreason. Furnished with these intellectual chymists, as they were called, who pursued components, man is prepared to compete these experiments, had another object in with his fellows, and to assume his rank view, namely, the discovery of an universal among intelligent beings. He has now ac- remedy. With regard to the first of these quired the elements, from which his mind objects, the transmutation of the metals, it may proceed to the display of reason, and to is not surprising that they should conceive the elaboration of thought. He is now suffi- such a thing possible, especially when you ciently instructed to survey the world in retiect on the separation of the metals from which lie exists, and to comprehend the acts their ores, and that from many of these, recesses.

Property comprises vegetable,

all the

ducts of the animal,

independent

;,

77

unpromising bodies in appearance, together, so as to form a system of chemistry, of the most valuable metals are obtain- the first of the kind, which was published ed, as is the case with iron, which they suc- in France, in the year 1777. Dr. Priestley, ceeded in reducing from what in appearance about the same time, made a numbei of very are mere stony ores, and it seems to me that valuable acquisitions to the science, by the considering that they had transmuted these discovery of a number of gaseous or acribodies into iron, there was some plausibility form bodies ; for although it was known in the notion that they should be able to before his time, that there were two or convert some of the less precious into the three different kinds of air, yet they were You may also find a only regarded as atmospheric air, loaded more precious metals. similar explanation for the other object of with certain vapours. He pointed out their the alchymists. namely, the discovery of distinct nature, and you will find that the a panacea, or an universul remedy ; for, find- gaseous or pneumatic chemistry, as it was called, contributed a number of important ing that the metals possessed very powers in the cure of certain diseases, they facts to the science. Matters remained imagined that, having done thus much, they pretty much in this state, until the science might do more, and discover an universal received a new and very important stimulus in the early part of the present century, by remedy. It is to the labours of these persons, who the discovery of what has been called Galflourished in the middle or dark ages, that vanism ; or I ought rather to say, by the dischemistry is indebted for many valuable dis- covery of the relations of electricity to coveries ; they discovered a great number chemical changes. The discovery originated of the metals, many of the acids, many of with Volta, was improved upon by Galvani, the salts, and spirits of wine, which were and has been pursued by several experinot known at any previous period, and there- menters in this country, but especially by fore the origin of chemistry is undoubtedly Sir Humphrey Davy, to whose brilliant inwith the alchymists. But if you choose to vestigations on this subject, chemistry is trace the history of the science to a more mainly indebted for the great and rapid proremote period, you will find, in holy writ, gress which it has made in the last twentymention made of the fusion of different five years. metals from their ores, and so on, which imIt is not easy to give a very unobjecplies a degree of chemical knowledge ; but tionable definition of chemistry. Dr. Black the rationale of the process was then un- defined chemistry to be "a science which known. It was not, however, until a very us the results of heat and mixlate period, comparatively speaking, that ture upon bodies;" and, certainly, to exchemistry began to assume the form in amine into the changes produced upon heat and mixture, may be stated which we now find it, and to acquire a truly scientific aspect. There were, it is to be a main object of chemical investigation; true, many chemical facts distributed over but I should be inclined to make an addition a number of works, but the science appear- to this definition, and to say, that chemistry ed to proceed rather as a matter of choice is the science which teaches us to examine than of experimental inquiry. At the beinquire into the composition of bodies ginning of the last century, however, the generally, whether effected by heat and mixfacts discovered by the alchymists, were ture, or any other means; to inquire into gradually examined and classed, and re- the changes resulting from the mixture of examined upon scientific principles. Stahl bodies, and into the causes of these changes. and Beecher distinguished themselves in Accordingly, the chemist is enabled to diGermany, and in this country Drs. Hales, vide all bodies in this way, into two great Hooke, and Mayow, rendered many valuable classes, namely, into simple and into compound services to the science. Then if we take a bodies ; andin examining the various prostep to the middle of the last century, to ducts of nature, infinite as they appear to the period between 1750and 1760, we find be, we shall find that in the present state of that a number of persons, whose names are our knowledge, there are not more than very familiar to you, Priestly, Lavoisier, about fifty or sixty elementary or simple boand Cavendish, Scheele and Black, studied by the union of these, the chemistry upon very scientific principles, immense and diversified masses of matter and added exceedingly to the number of its upon the surface of the earth are formed. discoveries. They did more, however, than must not be confounded this, because they showed that chemistry with what the ancients called the elements, was capable of very numerous and valuable which you know were, according to them, applications to the arts, and they made such air, water, earth and fire, from they applications of it with great success. Soon supposed all other substances were formed; after the period last mentioned, Lavoisier nor the additions which the alchymists made explained a great numberof chemical facts, to those of salt, sulphur, and mercury ; but unknown before his time, and classed them we understand by the term, a number of es-

very

some

energetic

taught

bodies, by

and

dies,

that

The term element

which

78

sentially elementary bodies, the further decomposition of which has baffled our analytical skill. But, as you will by and by find,

called the attraction of cohesion ; but if I examine its composition minutely, I shall find that it is composed of carbonic acid and lime, and these are kept together by what is called chemical attraction or affinity, which will be described more at length in the next lecture. Sometimes this attraction takes place without producing any regular form in the shape of the body, at others, the most beautiful regularity may be observed; and in crystallisations you have examples of this. Now it is the business of the chemist to study these forms, and to investi. gate, as far as he can, the causes of these forms, because they assist him in arriving at a knowledge of the nature of their composi. tions. In examining into chemical affinity, we shall make you acquainted with the ge. neral terms usually employed, and with some of the common results of this species of attraction ; but here we shall only give you a general outline of the subiect, because the whole course will consist of tion of the causes and nature of chemical change, the result of chemical affinity, or attraction. Having thus examined attraction as causing chemical change, we shall proceed to examine how far it is influenced by heat; we shall endeavour to show that heat gives to bodies a repulsive energy and enables them to overcome the attraction of cohesion, and give examples of its power of converting solids in aeriform bodies. Our inquiries into the phenomena of heat will be first general, and then particular ; we shall examine its general effects in nature, and during the course shall trace its influence upon bodies more particularly. We then come to electricity as a chemical agent ; and here the chemist has great difficultv in draw. as ing the line between such are strictly chemical, and such as belong to mechanical philosophy, or to other branches of philosophical inquiry. However, we shall endeavour to point out the general phenomena of electricity, and the iiifiueiice which they exert upon chemical change. It was, as I have stated, at the comniencement of the present century that Volta made the capital discovery of the accumulation of electricity,by the contact of metallic substances. Volta hit upon a mode of accumulating the electricity thus produced by the contact of metals, and the instrument thus made has been since called the Voltaic pile, and from the share Galvani had in improving it, the Galvanic battery ; and it has been found to be a very useful instrument in prosecuting chemical inquiry. Now then these subjects, namely, attraction, heat and electricity, will, as I have stated to you, be brought before you generally at the opening of the course ; and they will constitute the first division of it. We shall then proceed

certain qualities in these bodies suspect that they are of a compound nature, and some chemists have gone so far as to consider their suspicions almost proof, and have called even the metals compound bodies from analogy. I shall, however, show you the necessity of adhering to matter of fact, and not to assume any thing which has not been proved by experiment. Chemistry being purely a science of experiment, it is impossible by deduction or mathematical inquiry, to arrive at the knowledge of a chemical fact. At the same time it is right to say, that the barriers between the several sciences are giving way ; and that chemistry is almost imperceptibly merging into mechanical philosophy. When you look at the number of objects presented to you by nature and art, and when you reflect that they are all of them matters of chemical inauirv. vou will be somewhat appalled at their number, and consider that the difficulty of arranging them is almost infinite. Arrangement and order will do a great deal in cases of this kind ; and I shall now proceed to show you the arrangement we shall adopt here ; not that I mean to say it is devoid of fallacy, but I consider it the best a teacher of chemistry can adopt. In the first place it is obvious that the chemist has to inquire into the powers which effect chemical changes. We have before us a number of simple or elementary bodies constantly assuming new forms, and we have to examine into the causes of these changes; we shall find them in the great powers or properties of matter of which we know nothing as to their cause, and these are attraction, neat, and electricity ; and it will be necessary to examine these powers generally as chemical agents, and afterwards their mode of action upon individual bodies. Now with regard to attraction, it is customary to divide it into homogeraeous and heterogeneo2cs, or into mechanical and chemical attraction. By the first term is generally understood that attraction which causes the particles of a body to adhere to each other ; and the same power which influences the particles influences the mass, and gives to bodies the power of what is called gravitation, preserving the planetary bodies in their proper movements and causing bodies projected from the earth to be attracted again towards its centre. Attraction opeiating on similar particles, causes adhesion of these particles ; and when acting upon dissimilar particles, produces chemical change. Here, for example, is a piece of white marble : if 1 throw it into the air, it is attracted toward the centre of the earth by gravitation, and its particles are held together by the same power, then to examine the materials upon which these we

often

see

which lead

us to

an explana-

phenomena

79 whichiodine, we shall examine the compounds which oxygen and chlorine form with each Now with regard to matter, it may be other, and in this way we shall avoid much divided into two great classes, the gaseous, of the perplexity in which the subject is highly attenuated and imponderable,to which usually involved. Having given you an acthe term radiant matteI’ has been given ; and count of the compounds of oxygen and chloI need only advert to light, to radiant heat, rine, we shall proceed to an examination of to the different rays of the prismatic flpec- iodine, and exhibit to you the compounds trum, to furnish you with instances of dif- which it forms with oxygen and chlorine. ferent kinds of radiant matter concerned in There are, perhaps, two or three other chemical changes and the influence it exerts bodies which belong to this class; as for on them. example, fluorine and some others ; but as Then in regard to ponderable bodies, they they have never been exhibited in a sepamay be divided into simple and compound ;,rate state, we cannot be certain of it, and infer that they belong to this class, from and upon this principle chemists and chehabitudes which they manifest in mical writers have founded their arrangement of different substances. They have combination. Then we come to the consideration of the described, first of all, the simple or elementary bodies, and in the next place the com- electro-positive bodies, or such as are attracted pounds resulting from their union ; and it by the negative pole, and you will find them was urged that this was the best way of to be hydrogen, which. is a gaseous body, the lightest in nature ; nitrogen, another making the student acquainted namely, first to describe the simple, and gaseous body, sulphur, and phosphorus, then the compound bodies. Another ar- solid, inflammable, and easily fusible bodies, rangement has been made of substances and carbon and boron inflammable, but ininto the sopporters of combustion and com- fusible bodies, or nearly so; and to this class bustible bodies; but I shall not stop to ex- may be added all the metals. I shall not, plain these now, and refer to them merely however, enter upon the consideration of to show you the classifications which have these now, further than to remark, that 1 been proposed. The basis of our arrange- there exists a great analogy between them, i ment of these substances will be founded and although each has some properties by upon their electrical relations ;and taking g , which it is distinguished from the others, them to be about flfty-four or sixty in num- yet that there are certain properties pos. ber, you will find that some of them are isessed by them in common, sufficient to conuniformly attracted by substances rendered stitute a distinct class, and one of these is positively electrical ; and we infer from cer- their attraction by the negative pole of an tain circumstances to be pointed out here- electrical apparatus. In the next place, we after, that they are naturally in an opposite shall examine hydrogen and its combination state of electricity. There are three simple with oxygen, so as to form water, which bebodies of the first kind,or supporters of com- comes an important subject of chemical inbustion ; namely, oxygen, which is a simple quiry, and the discovery of the composias one of the body in a gaseous form when uncombined; tion of which may be chlorine, also a gaseous body under common most important of modern times. Having

agents

are

and the them.

acting,

they produce

on

changes

we

certain

withthem,

regarded

circumstances, but existing as a liquid at done this, we shall proceed to its combina: very low temperatures, or under consider- tions with chlorine and iodine. Then we able pressure ; and iodine, existing as a solid shall take up nitrogen in the same way, and its union with oxygen will lead us to inquii e into the composition of atmospheric air, its propeities, and general characters and latitudes ; and so we shall go through the various substances, examining them first in their separate states, and then in their relationsa oxygen, then those of chlorine, and then the to each other. Now with respect to the properties of iodine, but we shall adopt a metals, these will form a very importar.t different plan ; for having described the feature in our inquiries ; they are a very sources and properties of oxygen, which by numerous class of bodies, and many of them. the way is a very important body, constitu- are of extreme importance in the arts, and ting a large portion of the ponderable mat- in medicine especially. The chemical hister of our globe, about a fifth part of the tory of the metals includes a number of colatmosphere and eight parts in nine of water ; lateral branches of inquiry, into which we liavidg, I say, pointed out its properties, we shall enter as far as our time will permit : shall proceed to examine chlorine in the in the first place we shall point out the state same way, to show you its sources and ge- generally in which they are found in the neral properties ; and then, instead of pass- earth in the form of mineral ores ; secondly,

Now we might show you that oxygen always permanently gaseous, and chlorine a liquid, and iodine a solid body; and that these three, which are electrio-negativp bodies, are always attracted by the positive pole. We might describe the properties of

body. is

ing on to the third body of this class,namely,.describe

their localities ; and. thirdly, the

80

general mechanical properties by which they It is necessary however for the chemist to in. distinguished from each other. This quire into these operations, which end in the constitutes a branch of science called mine- production of a variety of vegetable products, ralogy. Another collateral subject connected as gum, sugar, starch, acids, and alkaline subwith this, is the mode of extracting metals stances, and so on ; and a great variety of on a large scale from their ores ; the man- vegetable products will be examined in dener in which these are worked, and reduced tail, not merely regarding the mode of their to the state of purity in which they are formation generally, but also in regard to brought into the markets. The manner in their applications to the arts. which ores are reduced upon a large scale, I think necessary to state to you, that involves many processes, which will be the chemistry of the arts will be in all cases pointed out to you generally, and this branch entered upon as far as our time will allow ; is called metallurgy, or the extraction of and although the details of the workshop metals from their ores. Many of the metals cannot be gone into for want of time, yet combine with each other, and many of these we shall in all cases develop all the princombinations have been applied to most use- ciples of the arts, and show you some of ful purposes in the arts; and when speaking the manipulations, where they are imof iron, we shall explain to you its combi- portant, of the artist’s shop. Some of nation with carbon, so as to produce steel, these would require an entire course for and the various purposes to which such com- their elucidation ; take, for example, the arts of dying, bleaching, tanning, calicopositions are applied. We shall also have to describe their printing, and so on. We must adhere to the medical applications, which has been called abstract principles of the science, and go pharmaceutical chemistry, and part of the into their details as fully as our time will are

science is often spoken of as if it could be studied apart from the rest ; but it is only since pharmacy has been studied as a branch of general chemical science, that any true knowledge of it has been acquired. One of the most valuable discoveries, namely, the separation of the active principles of plants, as quinine from bark, morphia from opium, and so on, interesting to the philosophical chemist, and of great importance to the medical practitioner, may be pointed out to you as resulting from chemical investigation; these, however, will be pointed out more fully to you by and by. We might also advert to the treatment of persons poisoned by metallic substances, as illustrating the importance of a knowledgeof chemistry. In of the nature of many cases, oui the compounds formed by the union of the metals with different substances, will enable -us to discriminate such as are innocent from such as are hurtful, and teach us to prescribe accordingly. With the history of the metals, we shall conclude the history of the elementary bodies, and of their various mutual combinations, as far, at least, as they are independent of organisation; but we have for good reasons set apart those which are the result of life or organisation, as requiring a distinct and particular mode of investigation. We shall have to show you, that in the vegetable world, from the moment a seed begins to grow, it is performing a class of chemical operations upon the air and soil. But the mode of performing these operations is perfectly distinct from any thing that can be artificially represented, because they are under the influence of the vital principle of the plant, and consist in the selection of certain elements from the soil and air for its development and support.

knowledge

so that when you visit a manufactory, you will not be wholly ignorant of the principles of the processes which you may see then going forward. Another interesting branch of vegetable chemistry is fermentation, or the production of venous and acetous liquors from certain vegetable products. The principle of this change is simple enough ; but you will find that the causes of the various flavours of the wine and beer, andotherfermentedliquors, depend upon trifling circumstances,and are much under the control of the manufacturer, who adopts particular processes sometimes for particular ends. In regard to vegetable, as well as animal bodies, the modes of analysing them will be pointed out, and it may be well to state to you, that there are two modes of analysis resorted to, the one teaches us the nature of their ultimate parts, which we shall find to consist of carbon, hydrogen, and oxygen for the most part, and the mode of the relative quantities of these, will be shown ; and the other mode of analysis teaches us the quantity of gum, resin, sugar, and so on, in a body, which are called the proximate elements ; and in this way we shall arrive at a knowledge of the various vegetable and animal substances, distinguishable from each other by their chemical habitudes. Theold chemists had very little idea of the nature of animal substances ; they considered that they were composed of various materials, such as air, earthy matter, water, and oils, and so on, which they obtained by distillation ; but of late animal chemistry has acquired considerable interest, and has been studied upon more philosophical principles. In examining animal bodies, our first question is, which are their ultimate compounds ? We shall find that

allow;

determining

81

they are few in number, but that the se- arts of manipulation ; but you will see them condary products to which they give rise, performed, and you will have an opportunity are very numerous : carbon, oxygen, hydro- of examining the apparatus for effecting the

gen, and nitrogen, being the ultimate elements ; and proximate elements, albumen, jelly, fat, different acid and alkaline substances, and so on. We shall show you the mode of analysis by which all these may be obtained, the relations of these substances to each other, and the various circumstances under which they are applied in the arts, many of the arts depending, as I may say, upon the chemistry of animal bodies, as, for example, tanning, and so on. The functions of animals have been examined with great delicacy by different chemists, but unfortunately without any practical results as regards their application. Many of these, however, are still very interesting subjects of inquiry ; as, for example, the respiration, and to examine the change which the air produces upon the blood, which properly belongs more to the physiologist than the chemist ; but in consequence of the numerous experiments which have been made upon a variety of secreted fluids, we could not pass the sub-

analytical and other processes. As analytical tact, that can only be derived from experience ; and having made yourselves acquainted with the nature of bodies, you may acquire by practice that tact which belongs to the analytical chemist. These are all the general remarks I have to make on chemistry, and upon the plan of arrangement adopted in this school. There are one or two other subjects to various

to

which I wish to call your attention. During the course I may not be heard, or be perfectly understood on some points, from the pupil not being acquainted with the details brought before him ; I have therefore to request that the student will apply to have the subject cleared up to him after the lecture. In the next place I have to enjoin punctuality of attendance ; we shall be in our place at nine o’clock, and shall not detain you after ten. The necessity of punctuality in pursuing your studies must be so obvious to you, that I am sure I need only mention it to ensure attention to this

entirely. These investigations point. On Thursday we shall consider attraction commenced some time ago by Hales and Priestley, and have been repeated by generally, more especially in influencing Sir H. Davy, Drs. Bostock, Prout, Wollas- the forms of matter. It ton, and others of the present dav.

ject

over

were

was imagined that these investigations on respiration and secretion would have thrown LECTURE II. some light upon the nature of diseases ; and it was supposed that the analysis of Gentlemen,-In the former Lecture, the the blood in the healthy and diseased powers and properties of matter, as constate would point out many important nected with chemical changes, were briefly facts for the better treatment of diseases ; introduced to you under the titles of homobut, as I have told you, this unfortunately is geneous attraction, heterogeneous attraction, not the case, for there are so many impedi- or affinity, heat, and electricity. Now, of ments in the way of an accurate analysis ofcourse, I need only speak very generally of animal products as to baffle ail inquiries ofthe subject of attraction, because, during the this kind. With the chemical history ofcourse, you will have a series of illustrations animal products we shall conclude the of the effects of attraction upon bodies excourse ; and the geological lectures which hibited to you ; so that all I shall do, at prewere formerly given at its close, will be sent, will be to give a general view of the mixed up with the history of the metals in- subject, and to explain some of the terms stead of considering them apart ; because used in discussing the effects of attraction. to enter upon geology with success would As I have before said, we know nothing of

it. the cause of attraction, but that it is a kind to of power acting generally upon matter in two lectures, and therefore it was imper- mass, and upon its ultimate particles. Now, fectly discussed, so that we shall in the pre- in the former case, it is called gravitation, sent course offer you some geological re- and acts not only at sensible, but also at inmarks when considering the metals. sensible distances ; it controls the heavenly We have been frequently asked what part and planetary bodies-and, according to the of the course is to be set apart to analytical theory of Newton, were it not for the action chemistry. The fact is, that the whole ofof a power called inertia, which tends to hold the course may be considered as a develop- bodies in a state in which they are ment of the principles of this art, and the gravitation would cause the heavenly bodies application of these principles will be to run together, and form one mass. Graviobvious from the numerous illustrationstation is, therefore, restrained by inertia ; brought before you. It is quite impossible whilst that kind of attraction which acts to describe to the student in a lecture the upon the proximate particles of matter, hold-

require more time than we can devote to We were obliged to reduce the subject

put,

82

ducing crystals; and, in very many instances

ing them in contact, is called aggregatim, which power is opposed by heat and electrical agencies. You will observe, then, that the phenomena of nature depend on two great counteracting causes, the one acting in one direction, and the other in another ; the result being that harmony of action which nature everywhere presents. When attraction acts upon the proximate particles of matter, it is to be considered as modifying the texture and form of bodies, it gives a spherical figure to fluids, it tends to the adhesion or cohesion of surfaces, and when it acts on dissimilar particles of matter, that is, when it acts upon the ultimate elements properly so called, causing them to combine or unite, it constitutes chemical attraction, or chemical affinity. The term aggregation is applied to all those cases in which solid bodies are formed, and we say that the particles of this silicious earth (showing a piece of flint) are held together by aggregation ; we say, moreover, that they are held together by a strong power of aggregation, because the body is very hard ; but, on the other hand, if I take a piece of chalk, I find the aggregation of its

we

are

enabled to exhibit bodies m

a

crystalline form, which Nature does not pre-

in that state. On the other hand, nature produces many crystals which art has not hitherto been able to imitate. In order to obtain a body in a form, we must

sent to us

crystalline

its particles great freedom of motion, and this is done by a process of solution. Accordingly, if I pour water upon a piece of salt, nitre, for example, I find that the water will gradually act upon, and dissolve a portion of, it-or, in other words, the attraction of the water for the particles of the nitre overcomes their attraction for each other, and a portion therefore of nitre is taken up by the water, and combined with it in a state of solution ; but, after a time, the attraction of the particles of nitre for each other counterbalances the attraction of the water for them, and the mixture becomes quiescent ; the water will no longer take up any of the nitre, it has no longer any solvent power over it. If you now apply heat, which diminishes the attraction of the particles of nitre for each other, you enable the water to take up another portion of particles comparatively trifling; its particles nitre, and when that is done, the solution is The phenomena of are easily separated from each other, and said to be saturated. yet I have the same body, chemically speak- solution appear to depend upon the relative ing, but in different states of aggregation. attractions of the water for the particles of Here is a piece of marble, and here a piece the salt, which are counteracted by the atof calcareous spar, (showing them to the tractions of the particles of salt for each class,) bodies of very different degrees of’ other, and this attraction of the particles of hardness, the particles being held togetherabody for each other, often proves a great by various degrees of aggregation, but being, impediment to chemical action ; we are often notwithstanding, of one and the same che- obliged to powder them, in order to act upon mical nature. The term cohesion is employedthem chemically with greater facility. Havto signify that kind of attraction which is; ing, in this way, acted upon the nitre with exercised upon the surfaces of bodies. Ifcold water, I shall obtain a solution which you bring together two polished surfaceswill remain permanent ; the particles of will be diffused at particular distances you will find a strong tendency to adhere,nitre ii and the denser the bodies are, the strongerthroughout the water, and will have no tenis the cohesion of the surfaces. Now thiss dency to unite into a solid form ; but if you toheaion is not dependant on the air be-. diminish the quantity of water, you bring tween the surfaces, as was formerly sup-the particles of nitre nearer to each other, posed, since it will take place in vacuo.. and you give them a greater aggregating You generally observe the result of aggre-power, or tendency to unite. If you evaporate gation in producing masses of indefinitethe water to a certain extent, and allow the form ; large masses of matter cohere to-solution to cool without being disturbed, the gether, without any apparent order in theirparticles of the nitre then attract each other, arrangement ; but, in other cases, you findl and they do this according to regular laws, that the particles have arranged themselves! producing crystals of a certain definite form. in a Tegular order, and that this order is ai Now the regularity of the form of these mathematical arrangement constituting atcrystals will depend upon a variety of cirseries of forms usually called crystals-the; cumstances, but more especially upon the term applied to certain definite forms,, quiescence of the solution. If the solution which certain bodies are capable of as-be agitated during the process of cooling, suming. One thing must be attended to) the crystals will be very irregular, and of no in examining these bodies ; it is prettyconsiderable dimensions, because the agitaevident that, at one time, they must have; tion will prevent the aggregation of the parbeen in a liquid state, a state in whichtticles of the salt; but if you take pains with the particles composing them must havethe evaporation, if you suffer the water to enjoyed great freedom of motion. Now weescape slowly, keep the whole in a quiescent

first

give

II

are

capable, by artificial

processes, of pro-state, and operate upon

large quantities of

83

matter, you will find

difficulty in obtain- tity of water

as one of their elements, and this has been called the water of crystallisation, and that frequently in a very large quantity. The crystals of the sulphate of soda, for example, contain only 72 parts of the dry sulphate of soda, and 90 of water, making 162, which is the equivalent number of the crystallised salt ; and there is one appearance, and it would be very difficult to fact worthy of notice, that in the crystals of determine their form ; but if you allow the any one body, there is always the same crystallisation of the salt to go on slowly quantity of water entering into its compowithout being disturbed, you may obtain sition. You observe, therefore, that when large crystals, and you will find that each you obtain 162 parts by weight of the cryscrystal is a four-sided prism, terminated by tals of sulphate of soda, you have only 72 two dihedral summits ; and if you obtain a parts of the dry salt, the remaining 90 parts perfect crystal, you will find that the axes of being water, which will always be found in these two summits are opposed to each the same quantity in the same salt. Now, other. It may perhaps appear curious to when we wish to export salts, or to place you to describe the shape of a crystal, but them in as small a space as possible, we you will find that such information is very avail ourselves of the knowledge of this fact, valuable in determining the composition of and drive off the water of crystallisation, very many bodies. Now here are crystals well knowing that we can recrystallise the of nitre of different sizes, depending upon salt whenever we please, by again dissolving the degree of attention bestowed in their it in water. Some substances lose this preparation; and here you see a gigantic water of crystallisation very rapidly, on excrystal has been obtained ; and here you posure to air, the salt becomes opaque upon have a most perfect specimen of crystallisa- its surface, and pulverulent ; and such salts tion, a six-sided prism, with a dihedral sum- are said to efforesce:others, again, absorb mit. In preparing a solution for crystallisa- moisture from the atmosphere, and become tion, it is necessary to evaporate it down to liquid; such salts are said to be deliquescent; a certain point, before crystals will form some, again, as nitre, undergo no change on in it ; and when you have arrived at this exposure to air, and such are called permayou will find that numerous par- next salts. ticles of the salt begin to collect upon the You will find in crystallising salts consurface of the fluid, and form a sort of layer tained in aqueous solutions, that they someof salt, which is called a pellicleonly indi- times get a fit of obstinacy, and you cannot cating that a certain number of the particles get them to assume the crystalline form. I of the salt have overcome the attraction of have known this to occur more particularly the -water, and now begin to unite to each when operating on a large scale, and from other, a sure indication that you will have a some peculiar circumstances, from some crop of crystals when the liquid cools. state of the atmosphere, or from some cause There are some substances that you cannot or other, to the great loss of time and dissolve-as, for example, the metals in property of the manufacturer. This diffi. their pure state, but then you can melt culty may sometimes be overcome, by throwthem ; and if you pour out the interior of a ing some of the same kind of crystals into melted mass of metal, the interior of the the solution. You will find that the procavity will present a crop of crystals ; in cess of crystallisation is often accelerated, this way we can obtain crystals which we do by introducing some solid bodies into the not find in nature ; but there are many solution ; and the makers of sugar candy inmetals found crystallised in their native troduce strings into the saturated solution state, that we cannot procure at all by art. of sugar, on which the crystals become deThere is another way in which we often posited. A stick is often put into a solusucceed in procuring crystals, which is, in tion, and the salt separates upon it, and it is order to give their particles the greatest in this way that the baskets which you freedom of motion, they may be converted sometimes see are coated with crystals of into a state of vapour ; and you have a the sulphate of copper, for the purposes of familiar illustration of this mode of crystal- ornament. Here is a large crystal of citric lisation in the falling of snow, which pre- acid, which has been obtained by puttingaa sents a regular aggregation of the particles horse hair into a solution of the acid ; now, of water previously in a state of vapour. if you withdraw the hair when you see that The crystallisation of camphor on the sides a perfect little crystal has been formed, and of the vessels in which it is kept, is another then immerse it into a stronger solution, case of this kind. you may succeed in procuring a crystal of When substances have been crystallised considerable magnitude. in water, they generally retain a great quan. Now light has a most singular influence no

ing crystals in a state of great perfection. (Various specimens of crystallised bodies were shown.) To show you the influence of motion on the fluid during crystallisation, I may adduce the ordinary appearance of sulphate of magnesia, as it is used in pharmacy ; you know that the crystals have a fine silky

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upon the formation of crystals. If you take different substances, but still we find in some salt, and set the one different substances the rhomboids of the aside in a dark room, and expose the other same angles. It has been long known to to the light, you will find that the solution the cutters of gems, but especially to diaexposed to the light will crystallise more mond cutters, that they can only obtain perfectly than the other. If you put a basin smooth surfaces when the crystals are broken of salt in a room, and admit the light only in a given direction; and that if broken in through a small aperture, you will find that other directions, the fracture is irregular and the crystals run up the basin on the side uneven. Whatever may be the form of the exposed to the light, and vegetate, as it gem in its rough state, they can only were, in the basin in a most beautiful man- cut it down into the regular octohedron. ner. So that persons who crystallise salts Now the case is the same with calcareous are often obliged to do it in a free exposure spar, and use may perhaps render it more to light. There is another curious effect evident with a prism of this kind (showing produced on crystalline solution by the a wooden model of a six-sided priam). Now pressure of the air, at least this has been said. if we were to proceed carefully to the dis. If you take a solution of a salt of any kind section of such a prism with gentle strokes ready to crystallise, put it into a flask and of a hammer, we should find that only three cork it up, you will find that no crystals of the solid angles would yield at one exwill form so long as the air’s pressure is tremity, and that at the opposite extremity kept off, but the moment you withdraw the opposite angles would yield, and that the cork crystallisation commences. As you alternately. see here (the experiment was shown), Now these angles always have regular during the crystallisation there is a con- surfaces yielding planes, turning toward the siderable MpttTMMM of the matter contained primitive form of the crystal, generally at in the flask, and a certain quantity of angles of 450. If we go on breaking away, heat is evolved. How the admission of air one angle after another, we shall come causes the solution to crystallise we do not to this figure, which you see is again the know. It has been said that the crystal- shape of the original prism; continuing the lisation is produced by the air’s pressure; dissection of the crystal we arrive at the but pressure will not do it. It has also been rhomboidal figure, which is incapable of said, that it is occasioned by particles of affording any other rhomboids. We thus dust falling upon the solution ; but this is arrive at the primitive form of the calnot the case. Agitation or percussion will careous spar, which is always a rhomalso do it, and cause the particles of the salt boid, having obtuse angles of 1050. 5 m., to unite, but it does not seem a satisfactory and you will find that each fragment you explanation to say, that the admission of have removed presents some compound of the particles of air produces the same effect. the rhomboidal form. It is an object of Now, in regard to crystallisation gene- some importance with mineralogists to be rally, but more especially in regard to the able to determine the angles of the different formation of natural crystals, there is a cu- crystals, since, as it has been before observed, rious fact which has long attracted the at- several crystals present the same primitive tention of chemists and natural form with different angles. For the purpose of measuring these angles accurately, inphers, namely, in regard to what is the theory rf cI’ystallisation. Of this bubject struments called goniomete1’s are used, and I can only give you a hasty outline, as it of these there are two kinds. The simplest would consume a great deal of time to go consists of a semicircular scale of degrees, into all the details. However, I shall de- and a small pair of compasses destined to vote the remainder of this lecture to the receive the crystal, one leg of’ which serves giving you a sketch of the theory. Now as a rad-ius by which the number of degrees this subject was first investigated by Rome is to be read off upon the scale. The best, de Lisle and Hauy. It was observed by however, is that invented bv Dr. Wollaston, Rome de Lisle, that on taking any number in which a ray of light reiiected from the of crystals of carbonate of lime of different surface of the crystal is employed as a raforms, that they might by careful mechanical dius, instead of the surface itself; it enables division be all reduced to a rhomboid; or us to determine the angles of even minute if he took a six-sided prism of calcareous crystals with great accuracy, and is called spar, he found that all the fragments were the reflective goniometer. But as happens of a rhomboidal figure. Hauy pursued these in many departments of science, some one investigations, and succeeded in dissecting discovers some fact that appears to vitiate a number of crystals, and in arriving at a all our former conclusions, so it has liapcertain number of primitive forms, as he pened here ; and accordingly Mr. Mitscherconsidered them. Now it happens that lich has found that heat interferes very many substances have the rhomboid for their much with the accuracy of the measureprimitive form, but then the angles differ in ment, by causingthe particles of the crystal two solutions of any

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expand equally. Now, then, how up by Mr. Daniell, and it appears that this are we to account for the great variety of hypothesis is better calculated to account secondary forms which these primitive forms for the formation of crystals than that of produce? Why this I shall endeavour to I Hauy. If you press balis of the same size make you understand, by using two or three i together upon the same plane, you have In following the equilateral triangles produced ; and if balls familiar illustrations. method just described, Hauy obtained six so placed were cemented together, and afterprimitive forms, from which he supposed all wards broken, the straight lines in which the secondary forms were made up. Now they would separate would form angles of A single ball let us take the dodecahedron with rhomboi- 60° with each other. dal faces, and see how its formation can be placed any where upon this stratum would He touch those of the lower balls, and the accounted for upon Hauy’s theory. states that the cube is its primitive form, planes touching their surfaces would inand that if you break it you find all its frag. clude a regular tetrahedron. Then, again, ments cubical ; but how can we understand in order to obtain an octohedron, you have how all its angles can be rounded off so as only to take four balls and place one upon to produce a dodecahedron ? 1 Why, Hauy says the centre of each surface, and you get the that the secondary forms are composed of elements of a four-sided pyramid ; you got certain decrements of the primitive mole- the elements of the octohedron. It will be, cules. He says, that the original cube of therefore, sufficient to solve the difficulty the dodecahedron is made up of a great num- of the primitive form of the fluor spar to ber of smaller cubes, and that if you place assume, that the ultimate elements of the a succession of cubes decreasing by regular octohedron and tetrahedron may consist of decrements upon each face of the primitive spherical particles. But to obtain all the cube, you will have a series of decreasing varieties of form we are obliged to call in layers of cubic particles upon each of its six flattened and elongated spheres, or more faces, which will become a dodecahedron if correctly, oblate and oblong spheroids, to the decrement be upon the edges. But if our assistance. Mr. Daniell found that if we substitute for our coarse work the more an amorphous piece of alum be immersed in delicate operations of Nature, you may ima- water, and left to remain quietly to dissolve, gine that it can take place without produc- that at about the end of three weeks it may ing any irregularity in the figures of which be observed to have been unequally acted we liawe spoken. Now you can easily ima- upon by the fluid, and that the mass will gine how in different shaped crystals the present the forms of octohedra and sections same primitive forms may exist, by recol- of octohedra, as it were, stamped upon its lecting that the decrements may go on regu- surface. larly upon the edges, and not go on regu- Mr. Brande displayed a diagram of the larly at the angles ; and that by irregular, appearance presented by the alum, and conintermediate, and mixed decrements, a great cluded by observing, that in the next lecvariety of secondary forms would be the ture he should take a general view of the results of chemical attraction. result. We now come to some of the difficulties to which this theory is open. If you take a piece of fluor spar, you will find that it may be broken into acute rhomboidal fragFOREIGN DEPARTMENT. ments, and these rhomboidal fragments may be again separated into tetrahedra and oc-I tohedra. It becomes a question which is the primitive form of the crystal, the tetrahedron, CHYLE OBSERVED IN THE VEINS OF THE or the octohedron. Seeing that neither of JEJUNUM. them can nil space without leaving vacuities, or produce any arrangement suffiBy Professor MAYER, of Bonn.* ciently tenacious to form the basis of a permanent crystal ; and it would be an absurFROM my own observations, as well as dity to say that they were both primitive those of Alagendie and Tiedemann, it has forms. To get over these and some other been proved that the veins of the intestinal difficulties, Dr. Wollaston proposed that the canal are capable of absorbing the different ultimate particles of the crystal should not fluids which it contains. That these veins be considered as geometrical also take up chyle, is certainly not to be deangles as 7-Iauy imagined, but that they nied, although the fact cannot be easily should be regarded as being spherical ; and demonstrated. Every piece of information, he set to work to show us, that all the varieties of the form of crystals might be pro* Tiedemann’s and Trieviranus’s Zeitsduced by a certain accumulation of these spheres. This subject was afterwards taken chrift für Physiologie, vol. i. p. 331. not to

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composed of